[PATCH 0/4] mm: misc cleanups from __GFP_UNMAPPED series

[PATCH 0/4] mm: misc cleanups from __GFP_UNMAPPED series

[Brendan Jackman]

In v2 of the __GFP_UNMAPPED series [0], we realised that some of the patches
could potentially be merged as independent cleanups.

These are all independent of one another, if you think some are useful
cleanups and others are pointless churn, it should be fine to just pick
whatever subset you prefer.

No functional change intended.

[0]: https://lore.kernel.org/all/20260320-page_alloc-unmapped-v2-0-28bf1bd54f41@google.com/

Signed-off-by: Brendan Jackman <jackmanb@google.com>
---
Brendan Jackman (4):
      mm: introduce for_each_free_list()
      mm/page_alloc: don't overload migratetype in find_suitable_fallback()
      mm: rejig pageblock mask definitions
      mm/page_alloc: remove ifdefs from pindex helpers

 include/linux/mmzone.h          |  9 +++--
 include/linux/pageblock-flags.h |  6 +--
 kernel/power/snapshot.c         |  8 ++--
 mm/compaction.c                 |  3 +-
 mm/internal.h                   | 14 +++++--
 mm/mm_init.c                    | 11 ++++--
 mm/page_alloc.c                 | 88 +++++++++++++++++++++--------------------
 7 files changed, 79 insertions(+), 60 deletions(-)
---
base-commit: 30424114b17dd65c098749cedcaef301c1dd2f86
change-id: 20260512-page_alloc-unmapped-prep-c3ae0381d58b

Best regards,
-- 
Brendan Jackman <jackmanb@google.com>

[PATCH 1/4] mm: introduce for_each_free_list()

[Brendan Jackman]

There are a couple of places that iterate over the freelists with
awareness of the data structures' layout.

It seems ideally, code outside of mm should not be aware of the page
allocator's freelists at all. But, this patch just doesn't hide them
completely, it's just a meek incremental step in that direction: provide
a macro to iterate over it without needing to be aware of the actual
struct fields.

Signed-off-by: Brendan Jackman <jackmanb@google.com>
---
 include/linux/mmzone.h  |  9 ++++++---
 kernel/power/snapshot.c |  8 ++++----
 mm/mm_init.c            | 11 +++++++----
 3 files changed, 17 insertions(+), 11 deletions(-)

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 9adb2ad21da599354600b48b4f3f9a4158efa049..1331a7b93f33c67c6e07df1fd8c5e4504dc28e80 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -177,9 +177,12 @@ static inline bool migratetype_is_mergeable(int mt)
 	return mt < MIGRATE_PCPTYPES;
 }
 
-#define for_each_migratetype_order(order, type) \
-	for (order = 0; order < NR_PAGE_ORDERS; order++) \
-		for (type = 0; type < MIGRATE_TYPES; type++)
+#define for_each_free_list(list, zone, order) 				\
+	for (order = 0; order < NR_PAGE_ORDERS; order++) 		\
+		for (unsigned int __type = 0; 				\
+		     __type < MIGRATE_TYPES &&				\
+			(list = &(zone)->free_area[order].free_list[__type], 1); \
+		     __type++)
 
 extern int page_group_by_mobility_disabled;
 
diff --git a/kernel/power/snapshot.c b/kernel/power/snapshot.c
index a564650734dcdceda7193ca3c1bc6b347cc1ec8b..d933b5b2c05d453bbda93c728136fc2a76758fc7 100644
--- a/kernel/power/snapshot.c
+++ b/kernel/power/snapshot.c
@@ -1244,8 +1244,9 @@ unsigned int snapshot_additional_pages(struct zone *zone)
 static void mark_free_pages(struct zone *zone)
 {
 	unsigned long pfn, max_zone_pfn, page_count = WD_PAGE_COUNT;
+	struct list_head *free_list;
 	unsigned long flags;
-	unsigned int order, t;
+	unsigned int order;
 	struct page *page;
 
 	if (zone_is_empty(zone))
@@ -1269,9 +1270,8 @@ static void mark_free_pages(struct zone *zone)
 			swsusp_unset_page_free(page);
 	}
 
-	for_each_migratetype_order(order, t) {
-		list_for_each_entry(page,
-				&zone->free_area[order].free_list[t], buddy_list) {
+	for_each_free_list(free_list, zone, order) {
+		list_for_each_entry(page, free_list, buddy_list) {
 			unsigned long i;
 
 			pfn = page_to_pfn(page);
diff --git a/mm/mm_init.c b/mm/mm_init.c
index bd466a3c10c8e204dddd881c5334364e3d47d612..db5568cf36e12b6fe52854b274fc331d9b36cac3 100644
--- a/mm/mm_init.c
+++ b/mm/mm_init.c
@@ -1429,11 +1429,14 @@ static void __meminit zone_init_internals(struct zone *zone, enum zone_type idx,
 
 static void __meminit zone_init_free_lists(struct zone *zone)
 {
-	unsigned int order, t;
-	for_each_migratetype_order(order, t) {
-		INIT_LIST_HEAD(&zone->free_area[order].free_list[t]);
+	struct list_head *list;
+	unsigned int order;
+
+	for_each_free_list(list, zone, order)
+		INIT_LIST_HEAD(list);
+
+	for (order = 0; order < NR_PAGE_ORDERS; order++)
 		zone->free_area[order].nr_free = 0;
-	}
 
 #ifdef CONFIG_UNACCEPTED_MEMORY
 	INIT_LIST_HEAD(&zone->unaccepted_pages);

-- 
2.51.2

[PATCH 2/4] mm/page_alloc: don't overload migratetype in find_suitable_fallback()

[Brendan Jackman]

This function currently returns a signed integer that encodes status
in-band, as negative numbers, along with a migratetype. Switch to a more
explicit/verbose style that encodes the status and migratetype
separately.

In the spirit of making things more explicit, also create an enum to
avoid using magic integer literals with special meanings. This enables
documenting the values at their definition instead of in one of the
callers.

Reviewed-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
Signed-off-by: Brendan Jackman <jackmanb@google.com>
---
 mm/compaction.c |  3 ++-
 mm/internal.h   | 14 +++++++++++---
 mm/page_alloc.c | 40 +++++++++++++++++++++++-----------------
 3 files changed, 36 insertions(+), 21 deletions(-)

diff --git a/mm/compaction.c b/mm/compaction.c
index 3648ce22c80728b894cffce502d8caa3e4532406..168e63940b78247e08aef8b177a4c68adb36db31 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -2340,7 +2340,8 @@ static enum compact_result __compact_finished(struct compact_control *cc)
 		 * Job done if allocation would steal freepages from
 		 * other migratetype buddy lists.
 		 */
-		if (find_suitable_fallback(area, order, migratetype, true) >= 0)
+		if (find_suitable_fallback(area, order, migratetype, true, NULL)
+		    == FALLBACK_FOUND)
 			/*
 			 * Movable pages are OK in any pageblock. If we are
 			 * stealing for a non-movable allocation, make sure
diff --git a/mm/internal.h b/mm/internal.h
index 5a2ddcf68e0b6d1a9fbaeae07670dd252729f96a..09931b1e535f3f71887b5b6473f93ed21a41c7e7 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -1104,9 +1104,17 @@ static inline void init_cma_pageblock(struct page *page)
 }
 #endif
 
-
-int find_suitable_fallback(struct free_area *area, unsigned int order,
-			   int migratetype, bool claimable);
+enum fallback_result {
+	/* Found suitable migratetype, *mt_out is valid. */
+	FALLBACK_FOUND,
+	/* No fallback found in requested order. */
+	FALLBACK_EMPTY,
+	/* Passed @claimable, but claiming whole block is a bad idea. */
+	FALLBACK_NOCLAIM,
+};
+enum fallback_result
+find_suitable_fallback(struct free_area *area, unsigned int order,
+		       int migratetype, bool claimable, int *mt_out);
 
 static inline bool free_area_empty(struct free_area *area, int migratetype)
 {
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index c9edffe968ac25b8cd9f6f983bf4c9ba21e73a11..91d83c967bd478982e0161a99d47d3a76bd89992 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2249,25 +2249,29 @@ static bool should_try_claim_block(unsigned int order, int start_mt)
  * we would do this whole-block claiming. This would help to reduce
  * fragmentation due to mixed migratetype pages in one pageblock.
  */
-int find_suitable_fallback(struct free_area *area, unsigned int order,
-			   int migratetype, bool claimable)
+enum fallback_result
+find_suitable_fallback(struct free_area *area, unsigned int order,
+		       int migratetype, bool claimable, int *mt_out)
 {
 	int i;
 
 	if (claimable && !should_try_claim_block(order, migratetype))
-		return -2;
+		return FALLBACK_NOCLAIM;
 
 	if (area->nr_free == 0)
-		return -1;
+		return FALLBACK_EMPTY;
 
 	for (i = 0; i < MIGRATE_PCPTYPES - 1 ; i++) {
 		int fallback_mt = fallbacks[migratetype][i];
 
-		if (!free_area_empty(area, fallback_mt))
-			return fallback_mt;
+		if (!free_area_empty(area, fallback_mt)) {
+			if (mt_out)
+				*mt_out = fallback_mt;
+			return FALLBACK_FOUND;
+		}
 	}
 
-	return -1;
+	return FALLBACK_EMPTY;
 }
 
 /*
@@ -2377,16 +2381,16 @@ __rmqueue_claim(struct zone *zone, int order, int start_migratetype,
 	 */
 	for (current_order = MAX_PAGE_ORDER; current_order >= min_order;
 				--current_order) {
-		area = &(zone->free_area[current_order]);
-		fallback_mt = find_suitable_fallback(area, current_order,
-						     start_migratetype, true);
+		enum fallback_result result;
 
-		/* No block in that order */
-		if (fallback_mt == -1)
+		area = &(zone->free_area[current_order]);
+		result = find_suitable_fallback(area, current_order,
+						start_migratetype, true, &fallback_mt);
+
+		if (result == FALLBACK_EMPTY)
 			continue;
 
-		/* Advanced into orders too low to claim, abort */
-		if (fallback_mt == -2)
+		if (result == FALLBACK_NOCLAIM)
 			break;
 
 		page = get_page_from_free_area(area, fallback_mt);
@@ -2416,10 +2420,12 @@ __rmqueue_steal(struct zone *zone, int order, int start_migratetype)
 	int fallback_mt;
 
 	for (current_order = order; current_order < NR_PAGE_ORDERS; current_order++) {
+		enum fallback_result result;
+
 		area = &(zone->free_area[current_order]);
-		fallback_mt = find_suitable_fallback(area, current_order,
-						     start_migratetype, false);
-		if (fallback_mt == -1)
+		result = find_suitable_fallback(area, current_order, start_migratetype,
+						false, &fallback_mt);
+		if (result == FALLBACK_EMPTY)
 			continue;
 
 		page = get_page_from_free_area(area, fallback_mt);

-- 
2.51.2

[PATCH 3/4] mm: rejig pageblock mask definitions

[Brendan Jackman]

- Add a PAGEBLOCK_ prefix to the names to avoid polluting the "global
  namespace" too much.

- This new prefix makes MIGRATETYPE_AND_ISO_MASK look pretty long. Well,
  that global mask only exists for quite a specific purpose, and is
  quite a weird thing to have a name for anyway. So drop it and take
  advantage of the newly-defined PAGEBLOCK_ISO_MASK.

Reviewed-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
Signed-off-by: Brendan Jackman <jackmanb@google.com>
---
 include/linux/pageblock-flags.h |  6 +++---
 mm/page_alloc.c                 | 18 +++++++++---------
 2 files changed, 12 insertions(+), 12 deletions(-)

diff --git a/include/linux/pageblock-flags.h b/include/linux/pageblock-flags.h
index e046278a01fa8c37d898df94114d088933b6747f..9a6c3ea17684d821fde9ec272b0802dfb78249a9 100644
--- a/include/linux/pageblock-flags.h
+++ b/include/linux/pageblock-flags.h
@@ -36,12 +36,12 @@ enum pageblock_bits {
 
 #define NR_PAGEBLOCK_BITS (roundup_pow_of_two(__NR_PAGEBLOCK_BITS))
 
-#define MIGRATETYPE_MASK (BIT(PB_migrate_0)|BIT(PB_migrate_1)|BIT(PB_migrate_2))
+#define PAGEBLOCK_MIGRATETYPE_MASK (BIT(PB_migrate_0)|BIT(PB_migrate_1)|BIT(PB_migrate_2))
 
 #ifdef CONFIG_MEMORY_ISOLATION
-#define MIGRATETYPE_AND_ISO_MASK (MIGRATETYPE_MASK | BIT(PB_migrate_isolate))
+#define PAGEBLOCK_ISO_MASK	BIT(PB_migrate_isolate)
 #else
-#define MIGRATETYPE_AND_ISO_MASK MIGRATETYPE_MASK
+#define PAGEBLOCK_ISO_MASK	0
 #endif
 
 #if defined(CONFIG_HUGETLB_PAGE)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 91d83c967bd478982e0161a99d47d3a76bd89992..5d6144c8860ed10fd641184f389c4953465d5178 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -364,7 +364,7 @@ get_pfnblock_bitmap_bitidx(const struct page *page, unsigned long pfn,
 #else
 	BUILD_BUG_ON(NR_PAGEBLOCK_BITS != 4);
 #endif
-	BUILD_BUG_ON(__MIGRATE_TYPE_END > MIGRATETYPE_MASK);
+	BUILD_BUG_ON(__MIGRATE_TYPE_END > PAGEBLOCK_MIGRATETYPE_MASK);
 	VM_BUG_ON_PAGE(!zone_spans_pfn(page_zone(page), pfn), page);
 
 	bitmap = get_pageblock_bitmap(page, pfn);
@@ -437,7 +437,7 @@ bool get_pfnblock_bit(const struct page *page, unsigned long pfn,
 __always_inline enum migratetype
 get_pfnblock_migratetype(const struct page *page, unsigned long pfn)
 {
-	unsigned long mask = MIGRATETYPE_AND_ISO_MASK;
+	unsigned long mask = PAGEBLOCK_MIGRATETYPE_MASK | PAGEBLOCK_ISO_MASK;
 	unsigned long flags;
 
 	flags = __get_pfnblock_flags_mask(page, pfn, mask);
@@ -446,7 +446,7 @@ get_pfnblock_migratetype(const struct page *page, unsigned long pfn)
 	if (flags & BIT(PB_migrate_isolate))
 		return MIGRATE_ISOLATE;
 #endif
-	return flags & MIGRATETYPE_MASK;
+	return flags & PAGEBLOCK_MIGRATETYPE_MASK;
 }
 
 /**
@@ -534,11 +534,11 @@ static void set_pageblock_migratetype(struct page *page,
 	}
 	VM_WARN_ONCE(get_pageblock_isolate(page),
 		     "Use clear_pageblock_isolate() to unisolate pageblock");
-	/* MIGRATETYPE_AND_ISO_MASK clears PB_migrate_isolate if it is set */
+	/* PAGEBLOCK_ISO_MASK clears PB_migrate_isolate if it is set */
 #endif
 	__set_pfnblock_flags_mask(page, page_to_pfn(page),
 				  (unsigned long)migratetype,
-				  MIGRATETYPE_AND_ISO_MASK);
+				  PAGEBLOCK_MIGRATETYPE_MASK | PAGEBLOCK_ISO_MASK);
 }
 
 void __meminit init_pageblock_migratetype(struct page *page,
@@ -564,7 +564,7 @@ void __meminit init_pageblock_migratetype(struct page *page,
 		flags |= BIT(PB_migrate_isolate);
 #endif
 	__set_pfnblock_flags_mask(page, page_to_pfn(page), flags,
-				  MIGRATETYPE_AND_ISO_MASK);
+				  PAGEBLOCK_MIGRATETYPE_MASK | PAGEBLOCK_ISO_MASK);
 }
 
 #ifdef CONFIG_DEBUG_VM
@@ -2130,15 +2130,15 @@ static bool __move_freepages_block_isolate(struct zone *zone,
 	}
 
 move:
-	/* Use MIGRATETYPE_MASK to get non-isolate migratetype */
+	/* Use PAGEBLOCK_MIGRATETYPE_MASK to get non-isolate migratetype */
 	if (isolate) {
 		from_mt = __get_pfnblock_flags_mask(page, page_to_pfn(page),
-						    MIGRATETYPE_MASK);
+						    PAGEBLOCK_MIGRATETYPE_MASK);
 		to_mt = MIGRATE_ISOLATE;
 	} else {
 		from_mt = MIGRATE_ISOLATE;
 		to_mt = __get_pfnblock_flags_mask(page, page_to_pfn(page),
-						  MIGRATETYPE_MASK);
+						  PAGEBLOCK_MIGRATETYPE_MASK);
 	}
 
 	__move_freepages_block(zone, start_pfn, from_mt, to_mt);

-- 
2.51.2

[PATCH 4/4] mm/page_alloc: remove ifdefs from pindex helpers

[Brendan Jackman]

The ifdefs are not technically needed here, everything used here is
always defined.

Switching to IS_ENABLED() makes the code a bit less tiresome to read.

Reviewed-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
Signed-off-by: Brendan Jackman <jackmanb@google.com>
---
 mm/page_alloc.c | 30 ++++++++++++++----------------
 1 file changed, 14 insertions(+), 16 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 5d6144c8860ed10fd641184f389c4953465d5178..2985ad0ab1044bdfda8ccc7aaed2ded19b5ac7ed 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -650,19 +650,17 @@ static void bad_page(struct page *page, const char *reason)
 
 static inline unsigned int order_to_pindex(int migratetype, int order)
 {
+	if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE)) {
+		bool movable = migratetype == MIGRATE_MOVABLE;
 
-#ifdef CONFIG_TRANSPARENT_HUGEPAGE
-	bool movable;
-	if (order > PAGE_ALLOC_COSTLY_ORDER) {
-		VM_BUG_ON(!is_pmd_order(order));
+		if (order > PAGE_ALLOC_COSTLY_ORDER) {
+			VM_BUG_ON(!is_pmd_order(order));
 
-		movable = migratetype == MIGRATE_MOVABLE;
-
-		return NR_LOWORDER_PCP_LISTS + movable;
+			return NR_LOWORDER_PCP_LISTS + movable;
+		}
+	} else {
+		VM_BUG_ON(order > PAGE_ALLOC_COSTLY_ORDER);
 	}
-#else
-	VM_BUG_ON(order > PAGE_ALLOC_COSTLY_ORDER);
-#endif
 
 	return (MIGRATE_PCPTYPES * order) + migratetype;
 }
@@ -671,12 +669,12 @@ static inline int pindex_to_order(unsigned int pindex)
 {
 	int order = pindex / MIGRATE_PCPTYPES;
 
-#ifdef CONFIG_TRANSPARENT_HUGEPAGE
-	if (pindex >= NR_LOWORDER_PCP_LISTS)
-		order = HPAGE_PMD_ORDER;
-#else
-	VM_BUG_ON(order > PAGE_ALLOC_COSTLY_ORDER);
-#endif
+	if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE)) {
+		if (pindex >= NR_LOWORDER_PCP_LISTS)
+			order = HPAGE_PMD_ORDER;
+	} else {
+		VM_BUG_ON(order > PAGE_ALLOC_COSTLY_ORDER);
+	}
 
 	return order;
 }

-- 
2.51.2